I am having problem configuring the etherchannel between these two switches.
3550 has two ports connected to 2950 (23and24). Show etherchannel on 3550 shows that everything is OK, channel is up, lights are green.
Show etherchannel on 2950 shows the same. All up. However, port 24 is amber and shut down. I get the message %ETHCNTR-3-LOOP_BACK_DETECTED on port 24 at 2950.